1. Field of the Invention
This invention relates to proportional controllers and particularly to proportional controllers utilizing the properties of thermoexpansive and electroexpansive materials. More particularly, this invention relates to proportional controllers of the type described which are particularly adaptable to regulating air flow to an engine.
2. Description of the Prior Art
Automotive engine cold-start and warm-up (fast idle) characteristics are known to depend upon adequate air flow and a proper air/fuel mixture to the engine. The air/fuel mixture to the engine may be controlled by a conventional carburetor, or by the more advanced electronic fuel injection systems that are well known in the art. Adequate air flow for these special conditions has in prior art systems been provided by a secondary bypass augmenting the primary throttled air supply. Generally, for a "cold start" condition substantially more air is necessary than for a warm up or "fast idle" condition. Thereafter, the "fast idle" amount of air should be reduced even further to a normal or "curb idle " when the engine has reached operating temperatures. It has been found that start-up and fast idle air flow may be advantageously controlled by a proportional controller type device. The particular proportional controller disclosed herein utilizes the characteristics of a substantially incompressible thermoexpansive fluid such as silicone, wax or fluorocarbon compounds and the characteristics of an electroexpansive material such as a piezoelectric stack to actuate the controller. The characteristics of the materials effect a proportional displacement of the controller whereby air flow to the engine is controlled. Prior art controllers for the purposes described have not used the combined characteristics of thermoexpansive and electroexpansive materials to control air flow to an engine during start-up and warm-up periods as does the present invention to be hereinafter described.